Based on the images and your comments, I would say that the wire splice you are holding in the first image with the thick brown and thin red wire would be where you want to connect your C wire.

Where does the C wire connect?

A common wire (C-Wire) provides Wi-Fi thermostats continuous power by connecting it to a heating and cooling system (e.g. furnace).

Where does C wire go on transformer?





A C wire transformer has two output wires; connect one wire to Rc terminal and the other wire to the C terminal of your thermostat. Once you finish this connection, plug the transformer into your mains power outlet. The installation is complete now and the thermostat will be powered upon switching ON the power outlet.

What does C wire connect?

A C-wire, or a common wire, runs from your low voltage heating system (24v) and carries continuous power to your thermostat. In today’s electric market, most newer heating and cooling systems have C-wires, which guarantees compatibility for the installation of all smart thermostats.

How do I know which wire is C wire?


Quote from Youtube video: So it's fairly simple to tell if you have a/c wire or not firstly the purpose of a/c wire is basically for the newer thermostats. As either has a backlit display or has Wi-Fi functionality.

Can you connect C wire to transformer?

If you have a heat-only system connected to your Sensi thermostat, an easy option for adding a common, or c-wire, is to install a 24 VAC wall plug-in transformer. Transformers with 150-400mA output are the most widely available online and easily provide sufficient power for the thermostat.

Why is my C wire not working?





Quick Check for an Existing C-wire:



If it has batteries, remove them. If the thermostat loses power it does not have a C-wire, and you may need an add-a-wire kit. If it doesn’t lose power, locate your breaker panel. Flip the breaker for the wall with the thermostat on it.

How do I know if my C wire is working?

You should see 24 Vac. It could be as high as 29 Vac when nothing is running, and nothing will be with your thermostat removed. If you have the voltage then the C wire is real and you can continue. If not consider having your system updated to include it.

What color is C wire?

Blue wires

Blue wires are also called “C” wires because they are the Common wire. C wires are necessary for any “smart” thermostat that needs to be connected to a power source 24/7, regardless of your heat pump type.

Should C wire have voltage?



The C wire, a.k.a. the “common wire”, allows a constant flow of 24 VAC (volts AC) power to a smart thermostat. However, the C wire doesn’t provide the actual source of power to the thermostat. The wires that provide the source of power are the R wires (or hot wires).

How long is a strand of C wire?

Blade size: length=65 mm, width=21 mm. Spacing of blades: 100 mm C/C. Coil diameter: 3′-2″ or 960 mm.

Can Nest thermostat work without C wire?

According to the Nest website, your Nest thermostat will work without a C-wire but specialists still recommend using an adapter if you can’t get a C-wire installed. If your Best thermostat will not receive a constant flow of power, it might not work properly and it runs out of power it will not work at all.

How do I know if my thermostat has C wire power?



Quote from the video:
Quote from Youtube video: Begin by putting one probe whichever probe you want on the rh wire and test every other wire with the other probe. One of the wires will show up is 24 volts and that is your c wire.

Where does my thermostat get power?

Most room thermostats on heating and cooling systems receive their 24V AC electrical power from a low voltage transformer that itself is usually found at the boiler or furnace (blue arrow in our photo at left).

Is com 24V the same as C wire?

The c wire is an extra wire that can be used to provide a return path for continuous 24V power for any application. It’s normally used to provide a return path to power the thermostat. The “c” stands for common. It is often labeled as “c” on thermostat backplates.

Can I use RC wire as C wire?

No the Rc is the red wire. You need 5 wires or more for this to run with all the functions. You can use one of the other wires but you have to drop control of the fan. It will only come on when furnace comes on.